More specifically, the invention relates to a pivot mechanism incorporating:                first and second juxtaposed parallel rigid plates, interconnected by a hypocycloid gear train, the first plate having first and second faces, and the said first plate being formed by a single piece having an outer circular toothing belonging to the said hypocycloid gear train and positioned on the said first face,        a first seat frame fixed to the first plate.        
The document FR-A-2 578 601 describes an example of a pivot mechanism.